1. Field of the Invention
This invention relates generally to the field of electrocatalysis. More specifically, the invention relates to a method of creating de-alloyed electrocatalytic nanoparticles.
2. Background of the Invention
Electrochemical cells are devices that use the process of changing oxidation sates, during chemical reactions, to generate electricity. An electrochemical cell contains two terminals, an anode, and a cathode. An oxidation reaction occurs at the anode while a reduction reaction takes place at the cathode. This results in electron flow from the anode to the cathode (or positive current in the opposite direction).
Fuels cells and batteries are examples of electrochemical cells. Batteries are closed systems, some of which could be recharged for reuse. On the other hand, fuel cells require fuel, which is depleted during operation and must be replenished. This fuel is electrochemically oxidized to produce electricity on demand. Ethanol, methanol, and hydrogen are some examples of fuel that have been used in fuel cells.
In fuel cells that use hydrogen as fuel, hydrogen is oxidized at the anode (i.e. hydrogen loses electrons) and the oxygen is reduced at the cathode, water is the only product of this reaction. This reaction has a potential to produce electricity at 1.23 V, which is the potential difference of the occurring half-reactions.
In hydrogen/oxygen fuel cells, the oxygen reducing reaction (ORR) electrode (cathode) catalyst material of choice has been platinum (Pt) for decades. The ORR on Pt, however, is very irreversible causing large over-potential which significantly reduces the fuel cell efficiency. Much research has therefore been dedicated to identify more efficient catalyst systems with reduced precious metal content and improved ORR activity to enable the path to fuel cell commercialization. Pt rich alloys, most prominently platinum-cobalt formulations, have shown promise with state-of-art activity improvements of up to a factor of 2.5-3 times over pure Pt metal. However, to date a catalyst capable of performing suitably for automotive fuel cell applications is lacking.
Consequently, there is a continuing need for better fuel cell catalysts and thus for: (i) synthesis of new materials with higher catalytic activity, (ii) new methods for synthesis, and (iii) methods that lead to efficient functioning of the catalysts.